Wired interface connected. Connection interfaces - varieties and applications

Since microelectronics is now used almost everywhere, and its development is proceeding at a high pace, a situation has arisen when many standards and data transmission interfaces are used simultaneously. Along with more modern interfaces, such as RS-485, rather old ones, such as RS-232, are also in use. Consider the features, advantages and disadvantages of several of the most popular of them.

RS-232

(Recommended Standard) is still used in many computer and digital devices, but modern equipment usually released with support for newer interfaces, since RS-232 does not always meet current requirements. The maximum data transfer rate is only 115 kbps, and the range is 15 meters. In practice, these values ​​are often even smaller. Data transmission is fully duplex, carried out by comparing the nominal value in the cable with the ground potential. Connection type: point-to-point. The main advantage of RS-232 is its simplicity and low cost.

RS-422

It can be used to organize communication lines for distances up to 1200 meters (sometimes even more). This full duplex interface is most often used to connect two devices over long distances, since in networks based on it, only one device can be a transmitter. Up to 10 receivers can be connected to each transmitter. The maximum data transfer rate reaches 10 Mbps. A twisted pair is usually used as a conductor, information is transmitted in a differential way, i.e. by measuring the potential difference between the wires of the twisted pair. This provides a fairly high protection against external interference and independence from the ground potential.

RS-485

It is very similar in its characteristics to RS-422, however, it has become much more widespread in all types of electrical engineering due to the fact that on its basis it is possible to build networks in which all devices can not only receive a signal, but also transmit it. This is achieved due to the fact that RS-485 is a half-duplex interface and devices do not conflict with each other. It also features a high maximum data transfer rate - 10 Mbps - and a communication line range - up to 1200 m. The network can have 32 devices with standard resistance indicators. If equipment with lower resistance is used, up to 256 subscribers can be combined into one network.

CAN

The CAN interface is a half-duplex interface with a maximum data transfer rate of 1 Mbps. As with RS-485 and RS-422, a differential pair is used for signal transmission. CAN is characterized by very high channel noise immunity and multi-level error checking, due to which the probability of their occurrence is almost zero. It is used for organizing networks, where communication reliability is required in the first place. Just like RS-485, CAN can have multiple transmitters. The USB interface has a very high data transfer rate, especially in the latest versions (USB 2.0 - 480 Mbps, USB 3.0 - 4.8 Gbps). But too small range limits its widespread use (about 5 meters). At using USB you can create a network of type: point-to-point.

Other types of interfaces are also used. It is impossible to say unequivocally which interface is the best. In each situation, it may be most appropriate to use different connection types.

And now consider the internal computer interfaces for data transfer.

Both laptops and desktop computers are equipped with a huge number of connectors. It is not always easy for a beginner to understand them. The accompanying manuals usually do not contain full information about the purpose of all slots. We offer you an extensive article with illustrative illustrations to deal with the problem of connectors once and for all.

In fairness, I would like to note that it is very difficult to connect the device to the wrong connector. All of them are different not only in purpose, but also in form, so the erroneous connection of peripherals is practically excluded. Connecting the device at random is still not worth it. Every PC user should have at least a basic knowledge of the connectors in his computer.

All interfaces are divided into two types according to their location:

- external;

- internal.

Let's pay attention to the internal interfaces that are located directly in the PC case.

Internal interfaces

1. SATA

This is an improved version of the outdated ATA. Using SATA, drives are connected to the motherboard, for example, HDD. As a rule, this is an internal interface, but sometimes it is displayed outside.

2. ATA/133 (Parallel ATA, UltraDMA/133 or E-IDE).

This is a parallel bus. It is needed to transmit a signal from / to a hard and removable disks. There are forty contacts in the wire. With it, you can connect up to two drives simultaneously, operating in “slave” and “master” modes. The cable has a small protrusion on one side, making it simply impossible to connect it “wrongly”. However, old wires may not have such a protrusion, therefore, in order not to be mistaken, remember the rule. The colored strip applied on one side of the wire should match pin #1 on the motherboard.

3.AGP.

A special bus with which a video card is connected. AGP is considered outdated version, which was replaced by PCIe. However, this interface is quite common, as a huge number of platforms have been released for it. The interface has several versions, the latest of which - AGP 8x - has a bandwidth of 2.1 GB / s.

4. PCI and PCI-x.

Standard parallel buses that connect network and sound cards, modems, video capture boards. The most popular among users is PCI bus 2.1s throughput up to 133 Mbps. PCI-X has this ability much higher, which is why it is used on motherboards of workstations and servers.

5. PCIe.

With the tires described in the fifth paragraph, it is connected only by a similar name. This is not a parallel, but a serial interface. With it, you can connect graphic and other types of maps. PCIe provides twice the throughput of AGP. This is the latest among graphics card tires.

6. AMD power connectors are as follows: Socket 462, Socket 754, Socket 939.

Connectors for Intel: Socket 370, Socket 423, Socket 478, Socket 775. All but the last one have ATX12V 1.3 or higher power supply standard. Socket 775 has ATX12V 2.01 or higher.

Let's move on to external interfaces.

External interfaces

1.USB connector.

Using the Universal Serial Bus connector, you can connect many additional devices: keyboard, mouse, camera, printer. There are three types of interface:

A) "type A" (located in the PC);

B) "type B" (located on a removable device);

C) mini-USB (digital cameras, external hard drives and etc.).

2. "Tulip" (Cinch / RCA).

These connectors are color coded differently depending on the type of signal being received (audio, video, brightness, etc.).

3.PS/2.

Connectors used in stationary computers to connect a mouse and keyboard. They are characterized by the following coding: green - mouse, purple - keyboard. If you mix them up, nothing bad will happen, just the connected devices will not work. To remedy the situation, simply swap the plugs.

4.DVI.

Monitor slot that transmits digital signals.

5. VGA.

Connect a monitor using the Video Graphics Array connector. It is designed to transmit information in blue, green and red colors.

6. RJ45 for LAN and ISDN.

The network port used to connect to the Ethernet.

7. RJ11.

The port used to connect the modem. Similar to RJ45 but with fewer pins.

8.HDMI.

This is a multimedia digital connector that is designed for HDTV signals with a maximum resolution of 1920x1080. It has a built-in copyright protection mechanism (DRM). Interestingly, the length HDMI cable cannot exceed fifteen meters.

9. Scart.

This is a combo jack that combines RGB, S-Video and analog stereo signals.

10.S-video.

The 4-pin plug accepts color and brightness signals.

The router is the main component local network and performs most of the basic functions in data exchange. Not only the possibilities of your home network, but also its performance and stability. Therefore, his choice should be taken very seriously.

Introduction

In the first article in the article series, we found out that the router is the main component of the local network and performs most of the basic functions when exchanging data. And if so, then his choice should be taken very seriously. It is on it that many of the capabilities of your home network, its performance and stability will depend.

To make it easier for you to choose this complex device, let's look at the main characteristics of routers and see what they are responsible for. I will deliberately simplify some of the formulations when describing certain functions, trying not to overload the complex technical information inexperienced users.

Router types

In general, routers can be divided into two large groups - wired and wireless. Already by the names it is clear that all devices are connected to the first ones only with the help of cables, and to the second ones, both with the help of wires and without them, using radio WiFi technology. Therefore, at home, it is wireless routers that are most often used, which allow providing Internet and networking computer equipment using various communication technologies.

Conclusion 1: If you are not pursuing any specialized tasks, then it is better to buy a wireless router. This universal solution will allow you to network equipment using various data transmission technologies.

Wired connection interfaces

To connect computers and other devices using wires, routers have special T-shaped sockets called ports. In models focused on home use usually there are five - four LAN sockets (output interface) and one WAN or DSL (input interface).

The devices that you want to network are connected to the LAN ports, and the cable of the provider that provides broadband (high-speed) Internet access through a dedicated channel is connected to the WAN port. By the way, that's why for many routers the WAN port is signed with the word INTERNET.

Unfortunately, in some regions, broadband network access is still not available or very expensive. In this case, the Internet connection can be made using a telephone line (DSL or ADSL). Then, the built-in DSL modem acts as an external (input) network interface in the router, and instead of the WAN jack, there is a connector for a telephone cable marked DSL or ADSL at the back.

Recently, the wireless method of connecting to the Internet is gaining more and more popularity. mobile technology 3G and LTE (4G), capable of providing high data rates. This is especially true for large cities with a good coverage area of ​​cellular networks.

If you plan just such a way to connect to the global web, then you need to choose a router with support for 3G / 4G USB modems or with an already built-in mobile modem. In the first version, the router is equipped with a USB port for connecting modems and built-in software support for their main models, full list which can usually be found in the user manual.

In the second case, where the modem is already built in, there is a slot for installing a SIM card from any operator. This option is universal, but not the only one offered on the market.

Often, routers with built-in 3G / LTE modems are offered by the providers themselves (operators cellular networks) as proprietary solutions. In this case, a separate purchase and installation of a SIM card is not required, since the device is already configured to work in a specific cellular network.

Conclusion 2: Before buying a router, you first need to decide on the company that will provide you with access to the Internet (provider) and find out which way to connect to global network they use.

Modern routers use two types of LAN technologies. The first, Fast Ethernet, allows devices to communicate on the network at speeds up to 100 Mbps. The second, Gigabit Ethernet - up to 1000 Mbps. If you plan to actively exchange big files between computers on your home network, for example, high-quality video, then choose a router with gigabit LAN ports (10/100/1000BASE-TX). If the main task is simply to provide Internet to all devices on the home network, then you can limit yourself to a budget solution with a 100-megabit output interface (10/100BASE-TX). Indeed, today in many regions of Russia the bandwidth of Internet channels of private users does not exceed 10 Mbps, and only in large cities the speed of access to world wide web can reach 100 Mbps.

Conclusion 3: In most cases, to provide Internet to all devices participating in the local network, a router with a speed of LAN ports 10/100 Mbps c. But for the active exchange of bulk data between computers on a home network, a router with the maximum speed of information transfer through LAN equal to 1 Gbps. But it will cost more.

Another important characteristic of the router that you should pay attention to is the throughput of the WAN interface. This applies to those who plan to connect to the Internet using broadband access capable of providing high speed information exchange. It is important to know that WAN capabilities in many budget router models (up to 2000 rubles) are limited to data transfer rates of 30 - 35 Mbps. This means that by purchasing such a router and connecting to the Internet, for example, at a speed of 60 Mbps, you will be able to use the channel’s capabilities only by half, and you will overpay money in vain.

Unfortunately, for some reason, manufacturers do not consider it necessary to inform users of the throughput values ​​of WAN ports in the official technical specifications of devices. Therefore, these numbers are not usually published in any of the descriptions of routers, including those provided by many computer stores. The only way out of this situation is to use the search necessary information in the Internet. Fortunately, finding it in most cases is not difficult.

Conclusion 4: Before buying a router, decide at what speed you plan to connect to the Internet. If the channel is wide (over 30 Mbit/ c), then be sure to find out the throughput WAN port of the selected model of your future router.

If in your area you can only connect to the World Wide Web through a telephone line, then you should not worry about the bandwidth of the incoming network interface. Almost all modern routers have support for the most advanced on this moment ADSL 2+ standard providing top speed incoming stream equal to 24 Mbps, and outgoing - 3.5 Mbps.

Wireless connection interfaces

As already mentioned, wireless routers contain a Wi-Fi module responsible for transmitting data using a radio signal. Most often Wi-Fi is used to connect various devices to a local network, but sometimes with the help of this technology wireless bridges, allowing you to connect subnets via a radio channel.

Strictly speaking, the abbreviation Wi-Fi refers to a set of standards wireless communication in local areas of IEEE 802.11, which was proposed and promoted by the Wi-Fi Alliance, after which it received its user name. It was not by chance that I mentioned the phrase “set of standards”, since modern routers use not one wireless data transmission standard, but several of its varieties at once:

• WiFi Standard 802.11a - data transfer rate up to 54 Mbit / s transmitted at a frequency of 5 GHz. Outdated standard;
• Wi-Fi Standard 802.11 b - data transfer rate up to 11 Mbps transmitted at a frequency of 2.4 GHz. Outdated standard;
• Wi-Fi Standard 802.11 g - data transfer rate up to 54 Mbps transmitted at a frequency of 2.4 GHz. To date, the most common standard, but already obsolete;
• Wi-Fi Standard 802.11 n - data transfer rate up to 150/300/450 Mbps transmitted at frequencies of 2.4 and 5 GHz. At the same time, in many cases, manufacturers in the specifications write doubled speeds (300/600/900), meaning the total values ​​of information transfer in both directions (reception and return). The modern common standard that is actively replacing 802.11g;
• Wi-Fi Standard 802.11 ac - data transfer rate up to 1300 Mbit / s transmitted at frequencies of 2.4 and 5 GHz. A very promising, but still uncommon standard.

All advanced standards have backwards compatible with older versions. For example, 802.11ac is backward compatible with 802.11a/b/g/n.

The most budgetary and common options are routers with support for Wi-Fi 802.11a / b / g technologies. No less popular are routers with Wi-Fi 802.11n, which provide a good coverage area and high data transfer rates. Well, the 802.11ac standard is still exotic, since the equipment supporting it is expensive and has not yet become widespread.

Recently, dual-band routers have become increasingly popular, the Wi-Fi module of which is capable of simultaneously operating at frequencies of 2.4 and 5 GHz. Both ranges have their advantages and disadvantages. The first (2.4 GHz) is compatible with all standard WiFi devices(smartphones, laptops, tablets, printers, etc.), but because of this it has high level channel noise. The second (5 GHz) provides a lower level of interference on the air, but the signal quality is highly dependent on line-of-sight and deteriorates greatly in the presence of a large number obstacles.

Conclusion 5: The most optimal purchase will be a router with support for 802.11 technology n compatible with old standards and high data rates. Dual band support wireless networks would be superfluous, although optional.

To ensure a high-quality radio signal when using Wi-Fi technology, most wireless routers are equipped with additional external antennas. Their number ranges from one to three, depending on the model of the router. In some cases, manufacturers may use internal antennas not sticking out from the outside. In most cases, this works general rule- the more antennas, the better the coverage.

Conclusion 6: It is hardly worth worrying about the number of antennas in the router for residents of Khrushchev and other small-sized apartments, but it is better for happy owners of large multi-room apartments or country houses to focus on routers with big amount antennas.

Additional connection interfaces

It is not uncommon for modern routers to be equipped with one or several USB ports at once, to which additional peripheral devices can be connected and accessed from the network. For example, you can connect a regular printer to the router and print documents on it from all devices on the local network or external hard drive for storing shared files.

Conclusion 7: If available in the router USB ports, you can connect various peripheral devices to them (printers, portable hard drives, disk storage NAS and others) and share them over the network.

Software

As you already understood, the router is a complex multifunctional device, which is a kind of mini-computer. And as in any computer, a special software called firmware.

A lot depends on the firmware, ranging from the stability of the device to its functionality. Thanks to the built-in software, the router implements various modes of its operation, mechanisms for protecting against unauthorized intrusions, support for methods of connecting to the Internet, and the ability to work with digital television and much more.

Poorly written firmware can turn even the most advanced router into a useless piece of hardware. So it’s better for especially meticulous users to immediately find out how high-quality software is in a particular router model before buying. This can be done on special forums and web resources.

In addition to the original firmware versions, for many router models there are so-called alternative versions firmware. They were written not by the developers themselves, but by enthusiasts and in some cases allow you to discover undocumented capabilities of devices, bringing them to a new qualitative level. The installation of such firmware is done at the user's own risk and peril, since after that the equipment loses the warranty. True, the situation can be corrected by re-installing the original firmware.

Conclusion 8: Functionality and the technical characteristics of routers depend not only on their internal "stuffing", but also on what firmware they are controlled by. good firmware can significantly speed up the operation of the router and expand its functionality.

Conclusion

On this, acquaintance with the main characteristics of routers can be considered complete. I hope the information received will be of good help to you when choosing a router on your own. Moreover, if necessary, the information provided in the "Wired connection interfaces" section will help you in selecting a switch, and in the "Wireless connection interfaces" section, in selecting an access point.

However, in this material, we have taken only the first step towards understanding such a complex device as a router. A router, even with the most advanced technical specifications, requires correct setting many parameters, but we will talk about this in a separate article.

Definition An interface is a standards-defined boundary between interacting information space objects. A method of exchanging data between a computer, device, or person. Consists of software and hardware parts. User interface - user interface - an interface that defines the processes of user interaction with an information resource.

USB The USB bus (Universal Serial Bus) - universal serial bus) appeared by computer standards quite a long time ago - the version of the first version of the standard was approved on January 15, 1996. The development of the standard was initiated by very reputable companies - Intel, DEC, IBM, NEC, Northern Telecom and Compaq.

USB The main goal of the standard is to create a real opportunity for users to work in Plug&Play mode with peripheral devices. This means that it must be possible to connect the device to a running computer and automatically recognize it immediately after connecting and installing the appropriate drivers. In addition, it is desirable for low-power devices to be powered from the bus itself. The bus speed should be sufficient for the vast majority peripherals. Along the way, the historical problem of lack of resources on the internal buses of an IBM PC compatible computer is solved - the USB controller takes only one interrupt, regardless of the number of devices connected to the bus.

Interrupt An interrupt is the termination of the execution of the current instruction or the current sequence of instructions to handle some event. special program interrupt handler, followed by a return to the execution of the interrupted program. An event can be triggered by an exception during program execution or by a signal from an external device. An interrupt is used to quickly react the processor to special situations that arise during program execution and interaction with external devices. The interrupt mechanism is provided by appropriate hardware software tools computer.

Specifications USB high speed exchange (full‑speed signaling bit rate) − 12 Mb/s; maximum cable length for high exchange rate - 5 m; low speed exchange (low-speed signaling bit rate) − 1.5 Mb/s; maximum cable length for low exchange rate - 3 m; maximum amount connected devices (including multipliers) - 127;

Specifications USB It is possible to connect devices with different exchange rates; no need for user installation additional elements, such as terminators for SCSI; supply voltage for peripheral devices - 5 V; maximum current consumption per device − 500 m. A (this does not mean that USB devices can be powered with common current consumption 127 x 500 m. A = 63.5 A). The design of the USB connectors is designed for multiple coupling/dismemberment.

USB topology This icon officially denotes the USB bus both in Windows and on the backs of computers, as well as on all USB connectors. This icon actually represents the idea of ​​the USB topology correctly. The topology of USB is practically the same as the topology of a conventional twisted-pair LAN, commonly referred to as a "star". Even the terminology is similar - bus breeders are also called HUBs.

Scheme USB connections devices to the computer Instead of any of the devices, there can also be a HUB. The main difference from the topology of a conventional local network is that there can be only one computer (or host device). HUB can be either separate, with its own power supply, or built into a peripheral device. Most often, HUBs are built into monitors and keyboards.

Cables and Connectors USB Schematic USB cable: GND - "case" circuit for powering peripherals; VBus +5 V − for power circuits; bus D+ - for data transmission, bus D - for data reception

Cables and Connectors USB cable to support full bus speed (full-speed) runs as a twisted-pair, shielded and can also be used for low-speed operation. The cable for operation only at the minimum speed (for example, for connecting a mouse) can be any and unshielded.

Cables and connectors USB connectors have the following pin numbering: Pin number Purpose Wire color 1 V BUS Red 2 D - White 3 D + Green 4 GND Black Shield Braid

Type "A" socket Type "B" socket Type "A" plug Type "B" plug

Which devices use or will use USB In low speed mode: keyboards; mice; joysticks; dot matrix printers; digitizers; digital cameras; modems for ordinary telephone lines; computer monitor control circuit;

Which devices use or will use USB In high speed mode: speakers; ISDN modems; external drives Iomega Zip class; PBXs; laser and inkjet printers; Photo video equipment; Drives; TV and FM tuners.

Development of USB - USB 2 standard. 0 In 1999, the same consortium computer companies, which initiated the development of the first version of the USB bus standard, began to actively develop version 2. 0 of USB, which differs in that the bus bandwidth is increased by 20 times, up to 250 Mbps, which makes possible transfer video data over USB, making it a direct competitor to IEEE-1394 (Fire. Wire). Compatibility of all previously released peripherals and high-speed cables is fully preserved, as well as one of the most important advantages of USB − low cost controller, which is also integrated into the chipset. Mass production of USB 2.0 devices began in 2001.

IEEE 1394 interface IEEE 1394 titles: Sony: i. Link, Apple: Fire. Wire, Toshiba: S 400 Others: DV in/out The standard for the cable part provides for three bus data rates - 98.304, 196.608 and 393.216 Mbit/s. Usually these values ​​in various documents are rounded up to 100, 200 and 400 Mbit / s, using the designations S 100, S 200 and S 400 for brevity.

Key Features IEEE 1394 data rates up to 400 Mbps according to the IEEE- 1394 a standard and 800 Mbps according to the IEEE- 1394 b standard agreed in 1394 Trade Association at the end of May 2001 ; The 16-bit address can address up to 64K nodes on the bus; maximum theoretical tire length 224 m; "hot" connection / disconnection without data loss; automatic configuration similar to Plug

The main characteristics of IEEE 1394 arbitrary bus topology - by analogy with local networks, both a "star" and a common bus can be used (only in the form of a chain, unlike a network on coaxial cable); terminators are not required at the end of the chain of connected devices; the possibility of exchange with a guaranteed bandwidth, which is essential for the transmission of video images; maximum distance between two devices in a chain according to IEEE- 1394 a - 4.5 m, according to IEEE- 1394 b - 100 m.

IEEE 1394 Topology The IEEE-1394 topology allows both tree and chain architectures, as well as a combination of both. Therefore, it is easy to build any options for connecting various devices. The standard provides for the architectural division of the bus into 2 main blocks - the cable part and the controller (s). So there can be several controllers, this part is also called the unifying part (backplane - literally the background, cross-board, etc.).

An example of a LAN topology on the IEEE- 1394 interface: DV (Digital Video) devices with the IEEE- 1394 interface

Compatibility For ease of programming and device compatibility, IEEE-1394 has developed a standard called the Open Host Controller Interface (OHCI). It imposes certain requirements on the registers of the IEEE-1394 controller and their memory mapping. In addition, an OHCI compliant controller must meet the power management requirements of the ACPI specification. Microsoft only supports IEEE-1394 OHCI compliant controllers in its Windows 98 Second Edition and Windows 2000 operating systems. hard drives operating system, for example, is not guaranteed.

Network on IEEE- 1394 V operating system Microsoft Windows Millennium Edition, released in the fall of 2000, introduced native support for IEEE-1394 controller-based networks for the first time. Such a network has a data transfer rate of 4 times faster than Fast Ethernet and is very convenient for a home or small office. the inconvenience in its construction lies in the small maximum length of one segment, only 4.5 m. To eliminate it, repeaters for 2 or 3 connections are produced.

IEEE- 1394 Cables and Connectors A standard cable for IEEE- 1394 consists of 2 twisted pair bus signal transmission, two power wires that are enclosed in a shielded sheath. Power wires are designed for current up to one and a half amperes and voltage from 8 to 40 V.

Cables and Connectors IEEE- 1394 6/6 wire cable, support up to 400 Mbps. Supply voltage up to 40 V at current up to 1.5 A. Length from 0.7 to 4.5 m. Cable for 6/4 wires, support for transfer rates up to 100 Mbps. Supply voltage up to 5 V at current up to 0.5 A. Length from 1 to 4.5 m. Cable for 4 wires, support for transfer rates up to 100 Mbps. Supply voltage up to 5 V at current up to 0.5 A. Length from 1 to 4.5 m.

Cables and Connectors IEEE- 1394 4-wire socket, support up to 400 Mbps. Supply voltage up to 5 V at current up to 0.5 A. 6-wire socket, support for transfer rates up to 400 Mbps. Supply voltage up to 40 V at current up to 1.5 A.

RS 232 (COM port) This equipment interconnection standard was developed in 1969 by a number of major industrial corporations and published by the Electronic Industries Association (EIA). The International Telecommunication Union ITU-T uses similar recommendations called V.24 and V.28 CCITT. In the USSR, a similar standard is described in GOST 18145-81.

RS 232 (COM port) The widely used synchronous and asynchronous serial interface was originally designed to connect a computer to a terminal. Currently found in a wide variety of applications. The RS-232 C interface connects two devices. The transmit line of the first device is connected to the receive line of the second and vice versa (full duplex). To control connected devices, software confirmation is used (introduction of appropriate control characters into the transmitted data stream). It is possible to organize hardware confirmation by organizing additional RS-232 lines to provide status and control functions.

Specifications RS 232 (COM port) Standard EIA RS- 232-C, CCITT V.24 Baud rate 115 Kbps (maximum) Transmission distance (maximum) Signal nature unbalanced voltage Number of drivers 1 Number of receivers 1 Connection scheme full duplex, point to point

Specifications RS 232 (COM port) Data itself (5, 6, 7 or 8 bits) is accompanied by a start bit, a parity bit and one or two stop bits. Having received the start bit, the receiver selects data bits from the line at certain time intervals. It is very important that clock frequencies receiver and transmitter were the same, the allowable discrepancy was no more than 10%. The RS-232 C baud rate can be selected from: 110, 150, 300, 600, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200 bps. All RS-232 C signals are transmitted at specially selected levels to ensure high noise immunity of the communication. Note that the data is transmitted in the inverse code (a logical one corresponds to a low level, a logical zero corresponds to a high level).

Specifications RS 232 (COM port) To connect an arbitrary RS to a computer via RS-232 C, a three- or four-wire communication line is usually used, but other interface signals can be used. Exchange via RS-232 C is carried out using calls on specially dedicated ports: COM 1 (addresses 3 F 8 h. . . 3 FFh, interrupt IRQ 4), COM 2 (addresses 2 F 8 h. . . 2 FFh, interrupt IRQ 3), COM 3 (addresses 3 F 8 h. . . 3 EFh, interrupt IRQ 10), COM 4 (addresses 2 E 8 h. . . 2 EFh, interrupt IRQ 11).